Device for forming concretions with regulated autonomous source

ABSTRACT

The invention relates to a device for forming concretions in an electrolytic medium by electrolysis, which comprises an anode 110 and a cathode 120 submerged in the electrolytic medium and a regulating circuit 100 configured to regulate an electrolysis current in order to form concretions on the cathode 120.The anode 110 and the cathode 120 are used as a current source for supplying the electrolysis process and are connected in the regulating circuit by at least one regulating element capable of limiting the electrolysis current.

TECHNICAL FIELD

The invention relates to a device for forming concretions with a regulated autonomous source.

TECHNOLOGICAL BACKGROUND

U.S. Pat. No. 4,246,075A discloses a device for forming calcareous concretions in a marine medium using electrolysis. This device uses an electrical source to produce a mixture of brucite and aragonite.

Patent application EP0152336 proposes a device for forming concretions using a sacrificial anode which maintains the electrolysis reaction until it dissolves.

Application WO2005/047571 discloses how to obtain a particularly hard aggregate using electrolysis controlled on the basis of an electrical source. This type of device uses cyclic regulation of electrode current and voltage to alternate between substantial formation of brucite and aragonite and partial dissolution of the brucite. The regulation takes account of a measurement of the electrolytic medium in order to determine thresholds for the formation of brucite and aragonite, such as pH, temperature, salinity, etc.

Thus, according to the prior art, there are devices that make it possible to form solid concretions but they use large energy sources which are relatively expensive and sometimes not very ecologically friendly. The use of a sacrificial anode makes it possible to overcome the problem of the electrical energy source. However, the concretions obtained are not sufficiently robust for seabed consolidation applications.

US2019/010614 discloses a device and a method for cathodically protecting and/or passivating a metal section in an ionically conductive material such as steel reinforcement in concrete or mortar. The device comprises an anode, for example a sacrificial anode, and a bar forming a cathode. The device comprises a transistor, for example a FET, and a resistor which generates a reference current for the transistor. Thus, the current is limited so as to keep it at a value which is suitable for cathodic protection while not being liable to damage the concrete or to discharge the cell prematurely.

SUMMARY

The idea underlying the invention is to propose a device for forming robust concretions without a large electrical energy source. The proposed solution is simply to use a sacrificial anode energy source and to regulate the current causing the anode to dissolve. Straightforward regulation or modulation of the electrolysis current makes it possible to obtain robust concretions.

According to one embodiment, the invention proposes a device for forming concretions in an electrolytic medium using electrolysis. The device comprises an anode and a cathode submerged in the electrolytic medium and a regulating circuit configured to regulate an electrolysis current in order to form concretions on the cathode. The anode and the cathode are used as a current source for supplying the electrolysis process and are connected in the regulating circuit by at least one regulating element capable of limiting the electrolysis current.

By regulating the current between the sacrificial anode and the cathode, it is possible to improve the formation of concretions by using a sacrificial anode as an electrolysis current source. In particular, it is possible to modulate this current, for example to compensate for the wear on the sacrificial anode. It is also possible to perform cycles for forming concretions by alternating periods of large current with periods of small, or even zero, current.

According to a first configuration, the regulating element may comprise a controlled variable resistance circuit for adjusting the current flowing between the anode and the cathode.

According to a second configuration, the device may comprise a plurality of anodes and the regulating element may comprise switches allowing the selection of one or more anodes for closing the circuit to the cathode.

In one particular embodiment, the first configuration and/or the second configuration may be carried out using MOS or MOSFET transistors, the channel of which is used as a variable resistor and/or operating as a switch. Thus, the device may comprise one or more anodes and the regulating element may comprise one or more MOS or MOSFET transistors placed between the anodes and the cathode.

Preferably, the device may comprise a control device, such as a microcontroller, which controls the regulating element in order to regulate the electrolysis current. According to one embodiment, the control device may be configured to regulate the electrolysis current according to an established time program.

The device may comprise an independent power supply for supplying the regulating circuit with electricity independently of the anodes and cathodes.

According to another embodiment, the anode and the cathode are used as the current source for the regulating circuit.

According to one particular configuration, the device may comprise an additional anode electrically connected to the cathode to provide a minimum concretion current. Advantageously, this additional anode may be used to supply the regulating circuit with power. In this case, the main anode is made of magnesium and the additional anode is made of zinc so that there remains a sufficient potential difference between the zinc and the magnesium for the regulating circuit to continue to be supplied with power.

According to one embodiment, the device comprises a battery for supplying the regulating circuit with electricity and a charge pump configured to draw electrolysis current and charge the battery.

In one preferred embodiment, the one or more anodes are made of magnesium, whether pure or impure, or of a magnesium alloy and the cathode is made of an iron alloy or copper alloy.

The device may comprise at least one current sensor and the current may be regulated according to the measured current.

The device may comprise at least one voltage sensor and the current may be regulated according to the measured voltage.

According to one embodiment, the control device is configured to modulate the control signal of the one or more transistors using pulse-width modulation (PWM) according to the established time program. In other words, the MOS is used in closed/open pulse mode and the opening rates are managed by the microcontroller, according to the principle of pulse-width modulation. This operating mode makes it possible to reach a target operating point while maximizing the energy efficiency of the system.

According to one particular embodiment, the control device is further configured to modulate the control signal for the one or more MOS or MOSFET transistors according to a measurement of the voltage across the terminals of said transistor when said transistor is open and according to the intensity of the cathode current, i.e. the intensity in the galvanic cell.

These two measurements allow the operation of the device to be adjusted via a feedback loop managed by the microcontroller.

The device may comprise at least one sensor for measuring at least one particular characteristic of the medium in order to provide regulation according to this measured characteristic.

According to one particular embodiment, the invention proposes a method for forming concretions in an electrolytic medium by means of a device as mentioned above, in which the device is placed in an electrolytic medium.

According to one particular embodiment, the electrolytic medium is seawater.

BRIEF DESCRIPTION OF THE FIGURES

The invention will be understood better and further aims, details, features and advantages thereof will become more clearly apparent from the following description of a number of particular embodiments of the invention, which are given solely by way of illustration and without limitation, with reference to the appended drawings.

FIG. 1 shows one exemplary implementation of a device for forming concretions.

FIG. 2 shows a first embodiment of a device for forming concretions.

FIG. 3 shows a second embodiment of a device for forming concretions.

FIG. 4 shows a third embodiment of a device for forming concretions.

FIG. 5 shows a fourth embodiment of a device for forming concretions.

DESCRIPTION OF THE EMBODIMENTS

In the description and the claims, the term “electrolytic medium” is used to refer to a continuous or discontinuous medium comprising salts in aqueous solution and in particular salts of calcium and of magnesium.

The coastline is not stable. Depending on the country, between a quarter and half of the coast is receding, thereby decreasing the land area. A sandy beach may recede by several meters during a heavy storm. A crumbly, rain-infiltrated chalk cliff may be undermined by high tides and collapse. Some coastal developments are endangered by this erosion. In addition, a rise in sea level is likely to amplify these erosion mechanisms.

FIG. 1 shows an example of riprap formed on a coast to reduce the effect of erosion. Concrete blocks 10 are deposited along the coast in order to break the waves and therefore limit the effect of erosion 11 which occurs on the coast. While the breakwater action is effective, there remains the problem of anchoring the concrete blocks 10 to the seabed. In general, the seabed is sandy and the surf tends to carry the sand out to sea, thus undermining the bed that supports the concrete blocks 10.

The device for forming concretions comprises a box 100, a sacrificial anode 110 and a cathode 120. The cathode 120 is placed at a location on the seabed where solidification is desired. The cathode 120 is connected to the box 100 to which the sacrificial anode 110 is also connected.

The cathode 120 is an electrical conductor on which the concretions are formed by electrolysis. The cathode 120 may be just an exposed conductive wire made of copper or of a metal alloy, for example stainless steel. Advantageously, the cathode is a lattice of conductive wires which makes it possible to have a larger electrical contact area in order to form a large calcareous matrix more quickly. The cathode is placed where it is desired to form the calcareous matrix, the shape of the electrode also determining the shape of the calcareous matrix.

The purpose of the sacrificial anode 110 is to generate the electric current in order to bring about calcium-magnesium precipitation on the cathode. Many materials can be envisaged such as, for example, alloys of zinc, aluminum, magnesium, whether pure or impure, and alloys of magnesium. For ecological and electrochemical reasons, it is preferred to use magnesium or alloys thereof.

Performing electrolysis using a magnesium sacrificial anode is done with a relatively low voltage of the order of one volt. The calcium-magnesium reaction produces brucite, Mg(OH)₂, and aragonite CaCO₃.

At a temperature of 20° C., brucite begins to form for a pH value of the order of 9.4 while aragonite begins to form for a pH value of 8.35. For the two precipitations of aragonite and of brucite, it is necessary to have a voltage of the order of one volt. In addition, increasing the voltage increases the pH and the amount of brucite and aragonite precipitated. The ratio of aragonite to brucite production changes according to the applied voltage. The use of a sacrificial anode does not allow the voltage between the electrodes to be acted on, only the current.

In order to create a harder amalgam, the box 100 regulates the electrolysis current in order to optimize the electrolysis current produced by the sacrificial anode 110. According to one embodiment, it is preferred to alternate cycles of brucite and aragonite formation with cycles of brucite dissolution. Thus, the amount of aragonite is increased by dissolving the brucite and therefore the solidity of the concretions produced is also increased.

By way of example, it is possible to alternate cycles of maximum current for one hour with cycles of eight hours of small or zero current. What should be understood by maximum current is a current of a few amperes to a few tens of amperes which depends mainly on the size of the area of the anode and of the area of the cathode. What should be understood by small or zero current is a current smaller than the maximum current so that the electrolysis reaction produces an aragonite-brucite mixture in the desired proportions. The small current may also be determined so as to adjust the pH of the seawater in order to dissolve brucite while maintaining minimal aragonite formation.

These cycles allow alternating phases of brucite-aragonite precipitation, ultimately creating geometric arrangements combining the two phases, resulting in interesting mechanical properties. Thus, the box 100 makes it possible to produce solid concretions with an energy input limited by the sacrificial anode, which is less expensive and more ecologically friendly.

A first embodiment is described in more detail with reference to FIG. 2. The box 100 comprises a control device which controls a variable impedance 210 placed between the anode 110 and the cathode 120. In the embodiment shown, the control device is a microcontroller 200. According to one embodiment, the microcontroller is a very-low-consumption microcontroller which is powered by a battery 205. In order to optimize the electrolysis reaction, a current sensor 220 measures the current flowing between the anode 110 and the cathode 120 and delivers this current measurement to the microcontroller 200. The current sensor 220 is, for example, a Hall effect current sensor. One or more sensors 230 are connected to the microcontroller 200 in order to deliver one or more items of information relating to the surrounding medium or to the behavior of the electrode-electrolyte interface, and allowing the electrolysis reaction to be optimized. A signaling circuit 240 is also connected to the microcontroller 200 in order to signal that the box is operational.

In embodiments which are not shown, the control device comprises analog components such as a clock and/or a counter.

The box 100 is a waterproof box intended to be submerged for several years. The choice of the microcontroller 200, of the battery 205 and of the other elements 210, 220, 230 and 240 must take very low consumption into account in order to have the longest possible service life. If the electrolysis cycle lasts several hours, it is then possible to decrease the clock frequency of the microcontroller 200 in order to decrease its consumption. In that case, putting the control-command part on standby between two setpoints may make it possible to highly advantageously decrease the self-consumption of the device.

Other choices may also greatly decrease consumption. The signaling circuit of a submerged box may transmit a radio signal in a widely spaced manner in order to signal that the box is operational. However, the transmission of a radio signal, even periodically, consumes a significant amount of energy. It is preferable to use a push-button, not shown, present on the box and actuable by a diver in order to trigger the illumination of an LED for a few seconds if the box is operational. Alternatively, it is also possible to use an inductive sensor capable of being actuated by a metal mass brought close by a diver. Such choices also make it possible to greatly decrease consumption.

In terms of consumption, the microcontroller 200 is the circuit which consumes the most. As a variant, it is possible to replace it with a simplified regulating circuit which consumes less than a microcontroller. In addition, the use of a microcontroller makes it possible to change a regulating program without the need to change a single element of the circuit. The microcontroller makes it possible to adjust the regulation of the current just before submerging the box if necessary.

With regard to the one or more sensors for the surrounding medium, the electrolysis reaction may be optimized according to pH, pressure, temperature, salinity, composition of the electrolyte, conductivity of the medium serving as the electrolyte or measurement of the polarization of the electrode-electrolyte interface. For a box intended to be permanently submerged at a depth of more than 10 meters, it is possible to assume that the medium remains stable and therefore not to use a sensor for the surrounding medium, the microcontroller 200 providing predetermined current cycles independently of any parameter of the surrounding medium.

According to another embodiment, the current sensor may be omitted and the microcontroller may perform current regulation only according to the measured parameters of the surrounding medium. By way of example, the microcontroller 200 may adjust the current to a maximum value which makes it possible to maintain the surrounding parameters below the brucite formation thresholds. The microcontroller 200 thus modulates the current according to the surrounding medium in order to keep the surrounding medium between the aragonite formation and brucite formation thresholds. However, without controlling the voltage of the sacrificial anode or all of the parameters to act on the surrounding medium, this type of regulation is not easy to implement.

As an alternative, the battery 205 could be omitted and replaced with a salt water battery dedicated to supplying the microcontroller 200 with power and comprising a dedicated anode and a dedicated cathode.

The box 100 of FIG. 2 comprises a variable impedance 210 coupled between the anode 110 and the cathode 120 and a current sensor 220 which measures the electrolysis current. Such a circuit makes it possible to regulate the electrolysis current to a maximum electrolysis value and a minimum electrolysis value. The sacrificial anode 110 should be sized so as to be able to obtain a current greater than the maximum electrolysis current that is desired so that the variable impedance may be adjusted in order to limit this current. Such sizing makes it possible to guarantee a constant maximum electrolysis current regardless of the wear on the sacrificial electrode 110. Specifically, the microcontroller 200 may adjust the value of the variable impedance 210 according to the maximum current that it is desired to obtain. If one or more sensors for the surrounding medium 230 are used, the microcontroller 200 may also adjust the electrolysis current according to the surrounding medium.

In this embodiment, the microcontroller 200 alternates the large electrolysis current and small electrolysis current cycles by adjusting the variable impedance 210 in order to obtain an adjusted maximum current and minimum current.

A second embodiment of the box 100 is shown in FIG. 3. In this second embodiment, a plurality of sacrificial anodes 110, 111 and 112 are used. A microcontroller 200′ has three outputs O1, O2 and O3 used to control switches 300, 301 and 302 serving to connect each of the anodes 110, 111 and 112 to the cathode 120. A current sensor 220, connected to the microcontroller 200′, measures the electrolysis current with which the cathode 120 is supplied. One or more sensors for the surrounding medium 230 may be connected to the microcontroller 200′.

In this second embodiment, controlled switches make it possible to adjust the current by connecting one or more sacrificial anodes 110 to 112 to the cathode 120. Each anode 110 to 112 that is connected creates a current proportional to the area of the sacrificial anode in contact with the electrolyte, which is seawater. The total current delivered may be limited by interference (coupling) with the neighboring anodes. Thus, it is possible to adjust the current to various levels according to what each anode can provide. In one particular example, the anodes are identical and are used singly up to a certain level of wear, and then they are used in pairs and then in threes.

In one variant, a fourth sacrificial anode 113 is permanently connected to the cathode 120 by means of a single connection wire 303 in order to provide a minimum current. This fourth sacrificial anode 113 may have an area in contact with the electrolyte that is smaller than the areas of the other anodes 110 to 112 so that the current is much smaller.

In another variant, not shown, this fourth sacrificial anode 113 is connected instead of the positive pole of the battery 205 and the negative pole of the battery 205 is connected to the cathode 120. Thus, the connection of the anode 113 to the cathode 120 is made via the microcontroller 200′.

A third embodiment of the box 100 is shown in FIG. 4. Two sacrificial anodes 110 and 111 are connected to the cathode 120 via the channels of two MOSFET (metal-oxide-semiconductor field-effect transistor) transistors 400 and 401. The gates of the transistors 400 and 401 are connected to a control circuit 410. The control circuit 410 is a device that allows a state to be memorized while the system goes into standby mode. To do this, the control circuit comprises a latch allowing a state to be memorized. This device must be able to receive, over two inputs, commands from two outputs O1 and O2 of the microcontroller 200″. A validation output OL of the microcontroller 200″ delivers a validation and memorization pulse which allows the control circuit 410 to memorize control voltages corresponding to the outputs O1 and O2 and to deliver said control voltages to the gates of the transistors 400 and 401. Thus, the microcontroller 200″ may be put into standby mode because memorization of the control voltages is provided by the control circuit 410.

The advantage of the third embodiment is that the transistors 400 and 401, by their MOSFET nature, may be used as switches and as variable resistances. MOSFETs have a channel resistance that varies depending on the gate voltage. In switching mode, it is preferable to use transistors that have a saturation resistance of the order of a milliohm. However, adjusting the gate voltage allows the channel resistance to be adjusted, which allows the current to be adjusted when the anode voltage is constant.

For optimum control of the MOSFETs, voltage and current measurements may be taken. Two analog inputs 11 and 12 of the microcontroller 200″ are connected to the drains of each of the transistors 400 and 401, respectively. These two analog inputs (11, 12) are used as voltage sensors to measure the drain voltage of each of the transistors 400 and 401. To provide current control, a shunt resistor 420 is placed in the path of the cathode current. One terminal of the shunt resistor is connected to an analog input 13 of the microcontroller 200″ in order to allow the cathode current to be measured. The shunt resistor 420 is sized to have a certain accuracy in measurement while achieving minimal voltage drop. A shunt resistor 420 of a few milliohms is suitable. The analog inputs 11, 12 and 13 of the microcontroller 200″ have an analog/digital converter which makes it possible to have an accuracy in measurement that is equal to the conversion step of said converter.

Thus, the microcontroller 200″ may turn off one of the transistors 400 or 401 in order to measure the voltage across the terminals and the current flowing through the other transistor 401 or 400 in order to measure the resistance of its channel. Taking a plurality of measurements corresponding to different gate voltages allows the microcontroller 200″ to have a characterization of the channel resistance as a function of the gate voltage for each of the transistors. After characterizing the channel resistances of the two transistors 400 and 401, it becomes possible to precisely adjust the gate voltages of the transistors according to the anode voltages and the cathode current according to the desired current.

In one mode of operation, the microcontroller is configured to modulate the control signal for the transistors 400, 401 in open/closed pulse mode, by applying the principle of pulse-width modulation. Voltage measurements are taken via the aforementioned analog input 11 or 12 of the microcontroller 200″ when the transistor 400, 401 connected to said analog input 11 or 12 is in an open state and current measurements are taken via the analog input 13 when the one or more transistors 400, 401 are in a closed state. The microcontroller regulates the pulse widths according to an established time program and the current and voltage measurements via a feedback loop managed by the microcontroller 200″. The average power delivered by the device depends on the pulse widths. In this configuration, resistive losses are almost zero, which preferentially optimizes anode consumption. Specifically, when the transistor 400, 401 is open, the only anode consumption is that of its self-corrosion value. When the transistor 400, 401′ is closed, the galvanic cell delivers the current required for the application (with a self-corrosion value that is non-zero but substantially decreased). This configuration is very highly advantageous in comparison with a variable resistor which would regulate the current delivered by the battery. This is because, in the latter case, the loss by Joule heating in the resistor or in the MOS used in its linear resistive range considerably decreases the efficiency, and therefore the service life, of the galvanic cell.

According to some embodiments, the device further comprises RLC electronic filters or other signal processing means in order to smooth the pulses generated by the transistors 400, 401.

In one simplified variant, the shunt resistor 420 may be omitted and the voltage between the one or more anodes and the cathode is measured when the transistors are open. The gate voltages of the transistors 400 and 401 are then adjusted according to the measured voltages which are also representative of the wear on the sacrificial anodes 110 and 111. The gate voltages of the transistors 400 and 401 may also be adjusted according to measurements of the surrounding medium using one or more sensors for the surrounding medium 230.

Note that, in the embodiment of FIG. 4, the microcontroller 200″ is powered by a salt water battery comprising a dedicated anode 431 and a dedicated cathode 432 which are intended to be submerged in an electrolytic medium, such as seawater. However, alternatively, the microcontroller 200″ may also be powered by a battery as for the embodiments of FIGS. 2 and 3.

A fourth embodiment is shown in FIG. 5. In this embodiment, the microcontroller 200″ is powered by a battery 500. Furthermore, a charge pump 510 is arranged to draw current between the anode 110 and the cathode 120 in order to charge the battery 500. The device and the capacity of the battery 500 are sized to ensure continuity of service of the control-command part. Advantageously, the charge pump 500 is configured to draw current and charge the battery while a small electrolysis current cycle is being applied. Furthermore, according to one advantageous embodiment, the microcontroller 200″ triggers a failsafe mode in which the charge pump 510 draws current and charges the battery 510 as soon as the microcontroller supply voltage drops below a first critical threshold and until it exceeds a second threshold, higher than the first.

This embodiment is advantageous in that the device automatically goes into service when it is submerged. The device may thus be pre-programmed and, for example, be embedded in the resin, only the cathode and the one or more anodes being intended to come into contact with the electrolytic medium. Thus, the immersion of the device into the electrolytic medium may allow the box to be activated as soon as it is submerged and to start up after a defined time delay.

This description refers to solidification of the seabed along a coast. The device for forming the concretions may also be used offshore or on any seabed serving as a support for a structure such as an offshore wind turbine, a lighthouse or a drilling platform. The device may also be used submerged in brackish water, in industrial fluids and in soils impregnated with an electrolytic liquid such as a marine soil, in particular.

Although the invention has been described in connection with a number of particular embodiments, it is obvious that it is in no way limited thereby and that it comprises all the technical equivalents of the means described and the combinations thereof where these fall within the scope of the invention.

In particular, although, in the embodiments described above, the device comprises just one cathode 120 associated with one or more sacrificial anodes, the device is liable to comprise a plurality of cathodes which are each associated with one or more sacrificial anodes through a respective circuit, the control device then being configured to simultaneously or successively control the various circuits.

The use of the verb “have”, “comprise” or “include” and of the conjugated forms thereof does not exclude the presence of elements or steps other than those set out in a claim.

In the claims, any reference sign between parentheses should not be interpreted as limiting the claim. 

1. A device for forming concretions in an electrolytic medium by electrolysis, which comprises an anode and a cathode submerged in the electrolytic medium and a regulating circuit configured to regulate an electrolysis current in order to form concretions on the cathode, in which the anode and the cathode are used as a current source for supplying the electrolysis process and are connected in the regulating circuit by at least one regulating element capable of limiting the electrolysis current, the device further comprising a control device which controls the regulating element in order to regulate the electrolysis current, the control device being configured to regulate the electrolysis current according to an established time program.
 2. The device as claimed in claim 1, wherein the regulating element comprises a controlled variable resistance circuit for adjusting the current flowing between the anode and the cathode.
 3. The device as claimed in claim 1, wherein the device comprises a plurality of anodes and wherein the regulating element comprises switches allowing the selection of one or more anodes for closing the circuit to the cathode.
 4. The device as claimed in claim 1, wherein the device comprises one or more anodes and wherein the regulating element comprises one or more MOS or MOSFET transistors placed between the anodes.
 5. The device as claimed in claim 4, wherein the control device is configured to modulate the control signal for the one or more transistors using pulse-width modulation according to the established time program.
 6. The device as claimed in claim 5, wherein the control device is further configured to modulate the control signal for the one or more transistors according to a measurement of the voltage across the terminals of said transistor when said transistor is open and according to an intensity of the cathode current when said transistor is closed.
 7. The device as claimed in claim 1, wherein the device comprises an independent power supply for supplying the regulating circuit with electricity independently of the anodes and cathodes.
 8. The device as claimed in claim 1, wherein the anode and the cathode are used as the current source for the regulating circuit.
 9. The device as claimed in claim 1, wherein the device comprises a battery for supplying the regulating circuit with electricity and a charge pump configured to draw electrolysis current and charge the battery.
 10. The device as claimed in claim 1, which comprises an additional anode electrically connected to the cathode to provide a minimum concretion current.
 11. The device as claimed in claim 1, in which the one or more anodes are made of magnesium and the cathode is made of an iron or copper alloy.
 12. The device as claimed in claim 1, which comprises at least one current sensor and in which the control device is configured to regulate the current according to the measured current.
 13. The device as claimed in claim 1, which comprises at least one voltage sensor and in which the control device is configured to regulate the current according to the measured voltage.
 14. The device as claimed in claim 1, which comprises at least one sensor for measuring at least one particular characteristic of the medium and in which the control device is configured to regulate the current according to this measured characteristic.
 15. A method for forming concretions in an electrolytic medium by means of a device as claimed in claim 1, wherein the device is placed in an electrolytic medium.
 16. The method as claimed in claim 15, wherein the electrolytic medium is chosen from seawater, brackish water, industrial fluids and soils impregnated with an electrolytic liquid. 